1. Field of the Invention
The invention relates to a method of producing a joint by introducing a flowable material such as a resin adhesive between components and is particularly, but not exclusively, concerned with a method of producing a joint using an adhesive, a sealant or a filler between aerospace components.
2. Discussion of Prior Art
Adhesive bonding for structural application uses film or paste adhesives.
Film adhesives are generally preferred for high performance applications and are easier to apply as they have little tack at ambient temperatures. They are however, more difficult to process as they need to be heated under pressure to achieve a bond. When using film adhesives the optimum glue-line thickness is approximately 0.2 mm.
Paste adhesives come in a variety of viscosities for different applications. One known process using a paste adhesive involves applying adhesive to the surfaces of the components to be joined and then, using a jig, bringing them together so as to form a sandwich, with the adhesive between them. The components must be brought together carefully to avoid entrapment of air in the adhesive between the components. Also, once together the components are difficult to adjust relative to each other due to the tacky thixotropic nature of the adhesive used and they need to be brought together accurately. The process is time consuming and is also messy and wastefull as adhesive extrudes from the sandwiched components as they are brought together. Due to the nature of the process, it is also labour intensive.
It is an object of the present invention to provide an improved method of bonding components.
According to an aspect of the invention there is provided a method of producing a joint, the method comprising positioning two components adjacent each other so as to define a space between them, bridging edges of the space with a sealing member and filling the space with flowable material such as a resin adhesive by suction.
The method of the invention is particularly straightforward and assemblies made with it can be manufactured slightly under design tolerance with the difference being taken up within the filled space. In addition, the method of the invention allows only one preparation, assembly and cure cycle to be used.
The use of the sealing member not only helps to keep the material in place at the edges of the space but may also control the profile of the material at the edges.
The sealing member may comprise a web, and is preferably retained in its bridging position using a fixing means such as an adhesive coating on a side of the sealing web. The web may instead be held in place by laying it against the components and painting over it with a sealant, for example PR 1875(trademark), an adhesive or a varnish. In the present example, the sealing web is constructed from fabric tape, although it may be constructed of other suitable material. The fabric tape may be constructed of glass or carbon fibres.
The components may be positioned adjacent each other using a construction jig.
It is desirable to have inlets at a low level and outlets at a high level to avoid resin/adhesive voids and porosity.
Paste adhesives are often used where the tolerances of the parts to be bonded are low but, even so, glue-lines (i.e. the thickness of the glue or adhesive layer between the components) greater than 0.5 mm have not previously been recommended using this method.
In order to address the problems that can arise with low tolerance components, a fabric of appropriate thickness may be placed in the space between the components prior to the filling of the space with the flowable material. That arrangement helps considerably to provide a strong joint line where the glue line is of substantial thickness and will avoid the need to utilise a member known as a xe2x80x9cshimxe2x80x9d between the two components. The flowable material introduced impregnates the fabric. With the use of the fabric the finished component will be analogous to a continuous composite, albeit cured at different times.
The fibre volume fraction for the joint may be substantially 2-70%, although preferably it will be substantially 30-60%. The fabric may comprise a lay-up of fibres such that fibres of one layer are transverse to fibres of another layer. Preferably the fabric will have a +/xe2x88x9245 degree lay-up. This orientation is springy and its fabric structure allows easy resin infusion therethrough.
If it is necessary to separate the components of the joint after the formation thereof, a release substance can be applied to a surface of one of the components which defines the space. The substance may comprise any convenient type of sealant material or a release layer. This technique allows very large areas effectively to be xe2x80x9cshimmedxe2x80x9d at the same time as bonding with no maximum thickness contraints.
Resins with low shrinkage, low coeffient of thermal expansion (CTE) and high strains are preferred, to minimise stresses. If a fabric is used it will preferably match the CTE of the components and will help control the overall CTE and thus minimise stresses. For CFRP the fabric would normally be the same type of carbon, whereas for hybrids or metallic construction glass may be preferred especially to avoid any galvanic corrosion problems.
In a further embodiment, at least one of the components has projections thereon, and the method comprises positioning the components adjacent each other so as to define a space between them with the projections extending into the space, the flowable material surrounding the projections as it is introduced into the space.
According to a further aspect of the invention there is provided a method of producing a joint, the method comprising providing first and second components at least one of which has projections thereon, positioning the components adjacent each other so as to define a space between them with the projections extending into the space, and introducing a flowable material such as a resin adhesive into the space to surround the projections.
One of the components may have the projections thereon, although both the components may have projections. Where both components have projections it is preferable that the projections on one component interdigitate with the projections on the other component.